The field of the invention generally relates to automatic clothes washers, and more particularly relates to method and apparatus for filling a wash tub with water having a desired temperature and level.
As is well known, automatic clothes washers typically have a control that permits the operator to select a desired water temperature. For example, in the most common arrangement, the operator has only three water temperature choices: cold, warm and hot. If cold is selected, the controller typically opens the cold water valve for the entire filling period. If hot is selected, the controller typically opens the hot water valve for the entire filling period. And if warm is selected, the controller typically opens the hot and cold water valves for the entire filling period to provide a water mixture of intermediate temperature. One problem with this arrangement is that it provides very poor temperature regulation, and thereby results in poor energy efficiency. For example, in average American homes, the water heater is set to about 130.degree. F. The cold water temperature in this same household typically varies between 45.degree. F. and 65.degree. F. as a function of the season. Thus, assuming a cold water temperature of 65.degree. F. and a hot water temperature of 130.degree. F., the warm water selection would result in a water temperature of 97.5.degree. F., assuming the warm setting resulted in a 50/50 mixture of the hot and cold water. If a particular detergent works best at 75.degree. F. and above, selecting a cold water wash (e.g. 45.degree.-65.degree. F.) would typically give poor washing results. However, selecting a warm water wash would typically result in wasting energy. In particular, a large part of the energy consumed in doing a load of laundry is used to heat the water. It is apparent that using 97.5.degree. F. water when 75.degree. F. water is sufficient results in a significant waste of energy.
In another prior art approach for controlling water temperature, a duty cycle was established for the hot and cold water. For example, an intermediate or warm water temperature was provided by cycling the cold water on and off with a duty cycle of 60%, and cycling the hot water on and off with a duty cycle of 40%. Therefore, wash or rinse water was provided at a temperature other than the mid-point between the hot and cold temperatures. However, the resulting temperature could not be accurately regulated to a desired temperature. Further, the on and off cycling caused wear and tear on the water valves, and reduced their life expectancies. Also, the cycling caused water hammer which is an undesirable thumping or pounding noise. The associated water impulse pressures can also lead to pipe and joint fatigue.
In still another prior art approach, a thermistor was positioned at the location where the water enters the wash tub to provide a measure of the temperature of the filling water. In response thereto, the valves were cycled on and off in an attempt to provide a desired temperature for water entering the wash tub. This approach had the same wear and water hammer drawbacks described above with regard to cycling on and off. Also, there was a tendency for this system to overcompensate.